Apparatus for cleaning gases with electrostatically charged particles



Feb. 9, 1 960 H F. JO'HNSTONE APPARATUS FOR CLEANING GASES WITH ELECTROSTATICALLY CHARGED PARTICLES Filed Jan. 21, 1958 18 Air wa INVENTOR. Henry ,7? J'ofuzst n United Stat APPARATUS FOR CLEANING GASES WITH ELEC- TROSTATICALLY CHARGED PARTICLES Henry F. Johnstone, Urbana, 111., assignor to the United States of America as represented by the United States Atomic Energy Commission Application January 21, 1958, Serial No. 710,368

' 2 Claims. (Cl. 183-7) This invention relates to the removal of aerosol particles and other finely divided suspended particles from air or other gases.

It is an object of the present invention to provide an apparatus for removing aerosol particles from gases.

It is a further object of the present invention to remove suspended material from air or other gases with the help of electrostatically charged solid pellets.

It is also an object of the present invention to remove suspended particles from air by combining the efiects of centrifugal force and electrostatic attraction.

These and other objects of the present invention are attained by my novel apparatus in which electrostatically charged small pellets are introduced into the center of a rotating body of the gas to be cleaned. Centrifugal force throws the small pellets to the edge of the rotating body. During their passage through the gas stream, they collect the suspended particles by electrostatic attraction.

The invention will now be described in connection with the accompanying drawing wherein Figure 1 represents a schematic view of my novel air cleaner and Figure 2 tube 14 to the walls of the cyclone, the pellets pick up and remove the fine particles from the air by impaction and by electrostatic attraction. The electrostatic charge on the pellets carrying the fine particles is removed partially or completely by grounding the wall. The pellets after striking the wall drop to the bottom of the cyclone carrying the aerosols with them and are discharged through outlet 12. If the pellets are not completely discharged, the walls of thecyclone 10 may be rapped or vibrated to assist inthe removal of the pellets from the walls and to ensure that they drop to the bottom of the cyclone. The pellets will remove both liquid and solid aerosolparticles from the air stream. i

It can be shown theoretically and has been shown experimentally that small pellets passing through a gas stream have a much higher efliciency for collecting aerosol polymerized styrene divinylbenzene rains,

The electrostatic charge on the pellets is directly proportional to the air rate and inversely proportional to the feed rate. I Table I shows the results of a-fewtests of the effect of the air rate and the feed rate on 'the charge 1 on the pellets. For these tests the charging conduit was is an enlarged cross-sectional view taken on line 22 of Figure 1.

In the drawing the numeral 10 represents a cyclone having a tangential inlet 11 near the bottom thereof. Cyclone 10 has a lower outlet 12 and upper outlet 13. An axially disposed feed tube 14 having a plurality of vertically disposed slits 15 therein is provided for the purpose of introducing small pellets to the center of the cyclone. Slits 15 are arranged spirally about the feed tube 14 and are located progressively closer nearer the bottom of the tube. Tube 14 is closed at the bottom. By this construction the number of small pellets leaving the tube 14 at difierent points is made relatively uniform. The slits penetrate the wall of the tube at a 45 angle to the radial, the direction being in the direction of rotation of the gas, as shown by Figure 2 of the drawing.

- The pellets are thereby directed into the whirling body of air to promote contact between the air and the particles. The pellets are kept in a hopper 16 and are conveyed pneumatically to cyclone 10 through conduit 17 by air from source 18. Baflies 19 are provided in conduit 17. These may be solid batlles which extend part way across the conduit 17 or may be screens which extend all the way across the conduit -17. The cyclone is grounded at 20.

Operation of the device will now be explained. Air or any other gas containing fine particles in suspension is introduced through inlet 11 and, due to its tangential introduction, flows upward spirally through cyclone 10 till it reaches outlet 13. Small pellets are introduced into conduit 17 from hopper 16 and are conveyed therethrough pneumatically. The pellets in passing through conduit 17 and impinging on baffles 19 pick up an electrostatic charge. The charged pellets then pass through tube 14 and slits 15 therein into the center of the rotating body of gas. Centrifugal force thereupon forces the pellets to the walls of cyclone 10. While passing from a 3 inch by 5 foot galvanized iron tube which enclosed a galvanized wire screen baffle. The importance of the bafile was demonstrated by removing it during a run. Without the baflle in the tube there was no measurable charge developed on the pellets.

TABLE -I Effect of air rate and Air Velocity, tt./sec. Feed Rate, Electrons per g./sec. PelletX10- B. PLASTIC PELLETS Tests to show the efiicacy of the process were made on an air stream within which aerosols of ammonium sulfite were generated. The aerosols were generated by injecting ammonia and sulfur dioxide through short sections of capillary tubing into air streams which were then mixed. The ammonia was introduced through a T-tube directed downstream seven feet from the acid gas inlet. Salt nuclei were injected into the main stream upstream of the ammonia and acid gas inlets. The cyclone employed was 18 inches in diameter and 5 feet high. The walls were 24 gauge galvanized iron. The air from a ZOOO-cu. ft. per minute blower entered tangentially atthe bottom and flowed upward spirally and set up a centrifugal force field which caused pellets introduced through A x 1% inch slits placed at a 45 angle in a Plexiglas (a polymerized methyl methacrylate resin) tube at the center to move towards the wall. The

Patented Feta/9, 196i) siits staited two inches abeve the tangential entrance and were continued tortwo feet with the-slits -beeom-ing- 1 furtherapart at the top of the tube. Electrification of the pellets was achieved by pneumatic conveyance through with water, dried, and "returned to the hopper for tee-' -10 cycle. Table II gives the details'of'thistest.

TABLE 11 Removal ofammom'um sulfite aerosols by charged pellets an me; 100 01111.]

AVGLASSPE'LLETS (30*40 MESH) Pellet Inlet Mass Feed Ammonia Medium Percent Run No. Rate, Ooncen- Dlameteri .Re-.

g./see. .tratlon, of Aerosol, move g./min. microns B. PLASTIC PELLETS (5 0-100 MESH) 3. 00 I 0. 0691 2; 60 41. 8 a. 10 1 0. 579 p 2. 70; 139. 5 a. 10 0.558 V 2.70. 38. 5 3.- 05 0552 1 3. 00 22.6 3; 42; 0. 608 '3. 10 20.5 3.42, 0.564 3.10 I 19.5

1 A, polymerized divlnylbenzeneres'in.

These results show clearly that good collection of aerosol "particles may .be obtained by electrostatica'lly charged: solid pellets. .Itis expected thathigher colloction efficiency would be obtained :withcyclones oflarge .1diam eter. 1

are sometimes encountered in the CottrelI device because of the -high voltages required -which-lead to insulation failure, and reentrainment of the dust already collected. Continual removal of the collected aerosol can be provided in my device. Much greater efficiency in the removalpf aerosols from a gas is obtained in'niy device than' in an ordinary cyclone. Par- .ticleswwhich arezso:srnall that theeificiency-ofan ordinary cyclone iswery :low lean be removed from air according to my invention with much greater elficiency.

-It will be understood thatthis invention: is not to be" limited to the =details given herein, but that it may be modified within the scope at the appended claims. What isclaimcdisz. L l t 1 1. In an air cleaner comprisinga cyclone having a tangential inlet, a lower outlefandan upper outlet, the improvement comprising a feed hopper for solid pellets, a feeding conduit in communication with said feed hopper, baflies in said conduit for ,electrostaticallycharg'ing the pellets {impinging thereon, a' feed "tube. extending axially of said cyclone in communication'withsaid conduit intdtlie center of "the cyclone.

'2. In an air cleaner'comprising a cyclone having a a tangential inlet, a loweroutlet' and an upper .outlet,the

improvement 'comprising afeed hopper for solid pellets,

a feding conduit-in communication with said feed 'hopthe pellets impinging thereon, 'a feed tube extending.

axially of said cyclone in communication with said'conduit, aplurality ofver'tically'disposed slits located in and arranged spirally aboutsaid feedtube, said slits "being located progressively closer nearer the bottonr of the feed tubeFand -peneti'ating the wall thereof at an angle tothei'aiiiztl such asrtoeject thepellets in'an oppositeldirection' to the direction ofrotat-ion of the gas,"anda source of-air for=blowing said fpellets into the center of the cyclone.

Ref er en'ces Cited in thefile of this patient I UNITED STATES "PATENTS -2;2s-1-,2s4 Anthony Apr. 28, 1942 FOREIGN PATENTS- 5,051 Great Britain Aug. '14, 191-4 "292,479

Great Britain June 13, "1929 

